Traffic parameter computer which measures the ratio of traffic volume measured at different locations



Ock. 3, 1%? J. H. AUER', JR 3,345,593

TRAFFIC PARAMETER COMPUTER WHICH MEASURES THE RATIO OF TRAFFIC VOLUMEMEASURED AT DIFFERENT LOCATIONS Filed Aug. 29, 1965 VEHICLE DETECTORSVr'Vg V +Vg INVENTOR. JHAUER JR. zmw/ v= TRAFFIC VOLUME V +Vz V=TRAFF|CVOLUME HIS ATTORNEY D l D FIG. 2

VEHICLE DETECTORS United States Patent TRAFFIC PARAMETER COMPUTER WHICHMEAS- URES THE RATIO OF TRAFFIC VOLUME MEAS- URED AT DIFFERENT LOCATIONSJohn H. Auer, Jr., Rochester, N.Y., assignor to General SignalCorporation, Rochester, N.Y., a corporation of New York Filed Aug. 29,1963, Ser. No. 305,357

8 Claims. (Cl. 235-150.24)

ABSTRACT OF THE DTSQLOSURE The disclosures relates to apparatus formeasuring the ratio of traffic volume measured at ditferent locations. Asignal accumulating means such as an operational amplifier receives apredetermined, uniform increment of signal in response to each detectionof a vehicle by a vehicle detector at one location. In addition, anamount of signal dependent upon the magnitude of signal in theaccumulating means is subtracted from the accumulating means in responseto each vehicle detected at another of the 10- cations. The magnitude ofsignals stored in the accumulating means is then representative of theratio of trafiic volume at the two locations.

Numerous instances arise when it is desirable to provide a voltageanalog of the ratio of traflic volume at a given location to totaltrafiic volume at a plurality of locations. For example, it may bedesirable to provide a voltage analog of the ratio of traffic movingalong a particular lane of a multi-lane highway to total traific alongthe highway moving in the same direction. In such instance, separatevehicle detectors may be positioned to sense traific moving in each ofthe lanes in the selected direction. Outputs of each of the separatevehicle detectors may then be applied to the computer of the instantinvention, which thereupon provides an output voltage analog of thepercentage of total-traffic moving in a particular direction along thehighway which is utilizing a particular lane of the highway. Obviously,such measurements are not restricted to trafiic moving in a singledirections, since trafiic moving in both directions may also bemonitored, and trafiic utilizing a single lane in either direction maythen be expressed as a percentage of total traffic utilizing the entirehigh-way, through use of the computer comprising theinstantinvention.

The invention is also useful for proving a voltage analog of the ratioof traffic volume in a particular section of a highway to trafiic volumein that section plus other sections of the highway. The computer mayalso be used for measuring the percentage of total highwayv trafficvolume entering or leaving at a particular access road for the highway.This would involve placement of vehicle detectors along the highway andthe access road. It is obvious that many other uses for this trafiicparameter also exist.

Accordingly, one object of the invention is to provide apparatus forcomputing the ratio of traffic volume sensed at one or more particularlocations to traflic volume sensed at one or more other locations.

Another object is to provide apparatus for producing a continuouslyvariable voltage of amplitude proportional to the ratio of trafiicvolume measured at a particu components to provide a voltage analogofthe ratio of traific volume at a particular location to traffic aplurality of locations.

Another object is to provide apparatus for computing volume at capacitor14 to capacitor 11.

In similar fashion, when relay R1 is energized, capaci- 3,345,503Patented Oct. 3, 1967 the ratio of the difference between trafiic volumesensed at two separate locations to the sum of traflic volume sensed atthe two locations.

Theinvention contemplates novel computing means for providing a voltageanalog of a trafiic volume ratio comprising amplifier means having aninput and an output, feedback capacitor means shunted across the inputand output of the amplifier means, means coupling a pulse of fixedamplitude to the input of the amplifier means in response to eachvehicle detection at locations providing numerator information for thevoltage analog, and means coupling a pulse of amplitude proportioned tooutput voltage amplitude of the amplifier means to the input of theamplifier means in response to each vehicle detection at locationsproviding denominator information for the voltage analog. The foregoingand other objects and advantages of the invention will become apparentfrom the following detailed description when read in conjunction withthe accompanying drawings, in which:

FIG. 1 is a schematic diagram of one embodiment of Y the novel trafficparameter computer.

FIG. 2 is a schematic diagram of another embodiment of the novel trafiicparameter computer.

Turning now to FIG. 1 there is shown an operational amplifier 10 havinga feedback capacitor 11 shunted across the input and output of theamplifier. A pair of vehicle detectors D1 and D2 are respectivelycoupled to relays R1 and R2 of the computer. These vehicle detectorspreferably comprise presence detectors such as those described in I. H.Auer, Jr. and H. C. Kendall Patent 3,042,303, granted July 3, 1962,although other types of vehicle detecting means may be usedsatisfactorily with the computer and it is by no means necessary thatthe detector be of the presence type.

The heels of a pair of contacts 12 and 13 associated with the relay R1are coupled to a pair of capacitors 14 and 15, respectively throughrespective resistors 16 and 17. Similarly, the heel of a contact 18associated with relay R2 is coupled to a capacitor 19 through a resistor20.

Front contact 12 of relay R1 is coupled to a source of positive voltage.Back contacts 12, 13 and 18 are each separately coupled to the input ofamplifier 10. Front In operation, each time a vehicle is sensed bydetector D1, capacitor 14 acquires a positive charge through resistor16. When the vehicle is no longer sensed by detector D1, relay R1deenergizes, coupling a positive charge stored on capacitor 14 to theinput. of amplifier 10.

Resistor 16 is sumciently small to permit capacitor, 14.to, charge to avoltage amplitude substantially that of the positivewoltage sourceduring the interval in which a vehicle is sensed by detector D1,regardless of speed of the vehicle, and similarly is sufficiently smallto permit substantially full discharge of capacitor 14 during theinterval in which relay R1 is denergized, regardless of how closelyeachvehicle follows the other in the stream of traffic belng sensed. Hence,each time relay R1 is deenergized, a fixed increment of c tor 15acquires a negative charge from the output voltage of amplifier 10.Again, it should be noted that resistor 17 is sufficiently small topermit capacitor 15 to .charge to a voltage equal to that stored acrosscapacitor 11 during the interval in which relay R1 is energized,

even when a fast-moving vehicle is sensed by detector D1. When relay R1deenergizes, capacitor 15 discharges,

providing a voltage pulse to the input of amplifier 10. This pulse tendsto decrease the voltage amplitude across arge is discharged fromcapacitor 11, since the polarity of voltage now provided from capacitor15 is of opposite polarity to the voltage stored on capacitor 11However, it should also be noted that when relay R1 deenergizes,capacitor 14 provides a charge to the input of amplifier of polarityopposite to that provided to the input of amplifier 10 from capacitor15.

In a fashion similar to that by which front contact 13 of relay R1permits charging of capacitor from capacitor 11 and back contact 13permits capacitor 15 to discharge to the input of amplifier 10, frontcontact 18 of relay R2 permits capacitor 19 to acquire a charge fromfeedback capacitor 11 during the interval in which a vehicle is sensedby detector D2, and back contact 18 permits capacitor 19 to discharge tothe input of amplifier 10 during intervals in which no vehicle is sensedby detector D2. Again, it should be noted that resistor 20 issufiiciently small to permit capacitor 19 to charge to substantially theamplitude of voltage stored across capacitor 11 when relay R2 isenergized and to permit capacitor 19 to substantially fully discharge tothe input of amplifier 10 When relay R2 is deenergized.

That the foregoing parameter computer provides an output voltage analogof the ratio of traffic volume sensed by detector D1 to traffic volumesensed by detectors D1 plus D2 may be shown in the following manner:

Let

Q =charge on capacitor 14 Q =charge on capacitor 15 Q =charge oncapacitor 19 C =capacitance of capacitor 14 C =capacitance of capacitor15 C =capacitance of capacitor 19 E=positive reference voltage amplitudeE =output voltage amplitude of amplifier 10 V =traific volume sensed bydetector D1 V traflic volume sensed by detector D2 T=a time intervalduring which vehicle detections are made n =number of Vehicles detectedby detector D1 during time T n =number of vehicle detected by detectorD2 during time T When a vehicle is sensed by detector D1 capacitor 14charges according to the equation and capacitor 15 charges according tothe equation Q2=C2E0 Similarly, when a vehicle is detected by detectorD2, capacitor 19 charges according to the equation During time T,charges Q Q and Q; are each multiplied by the number of vehicles sensedin that time by the respective detector producing the charge. Hence and( Q3 2 a o Since and 1 Vg-T 1 Equations 1, 2 and 3 can be rewrittenrespectively as Q1= 1 1 Q2= 1 2 o and ( Q3:V2C3E0 Since capacitors 15and 19 are both charged from output voltage E of amplifier 10, totalcharge applied to the input of amplifier 10 at equilibrium is equal tototal charge acquired at the output side of the amplifier during time T.Hence.

1 1 I Z O'l" a s o Then (7) E VICIE V C +V2C By making C C Equation 7can be rewritten as Therefore, since C C and E are constants, E isdirectly proportional to the parameter It should be noted that in orderto derive a volume ratio of to compare to rexample, relative trafiicvolumes at two different locations, it is merely necessary to open thecircuit comprising capacitor 15, resistor 17 and relay contact 13.

FIG. 2 illustrates a modification of the circuit of FIG. 1, wherein theoutput voltage analog produced by the computer represents the ratio ofthe difference between traflic volume sensed by detectors D1 and D2 tothe sum of traffic volume sensed by detectors D1 and D2. This isaccomplished by utilization of an additional contact 21 on relay R2, theheel of which is coupled to a capacitor 22 through a resistor 23. Backcontact 21 is coupled to the input of operational amplifier 10, whilefront contact 21 is coupled to a source of negative voltage, preferablyof amplitude equal to that of the positive voltage source.

Operation of the circuit comprising contact 21, resistor 23 andcapacitor 22 is substantially identical to operation of the circuitcomprising contact 12, resistor 16 and capacitor 14, with the exceptionthat capacitor 22 acquires a negative charge, while capacitor 14acquires a positive charge. Thus, when a vehicle is sensed by detectorD2, energizing relay R2, capacitor 22 acquires a negative voltagethrough front contact 21 in series with resistor 23. The amplitude ofthe acquired negative voltage is substantially that of the negativevoltage source, since resistor 23 is sufiiciently small to permitcapacitor 22 to charge to an amplitude substantially that of thenegative voltage source during the interval in which a fastmovingvehicle is sensed by detector D2. When detector D2 no longer senses avehicle, capacitor 22 discharges to the input of amplifier 10 throughback contact 21 in series with resistor 23, coupling a negative inputvoltage to amplifier 10. Moreover, capacitor 19 discharges to the inputof amplifier 10 through a back contact 18 in series with resistor 20,tending to decrease the magnitude of voltage stored on capacitor 11,regardless of polarity. This is so since the polarity of charge acquiredby capacitor 19 depends upon the polarity of voltage stored on capacitor11. Similarly, when relay R1 deenergizes after detector D1 has sensed avehicle, the polarity of charge coupled from capacitor 15 to the inputof amplifier 10 exceeds the number sensed by detector D2. Again, itshould be noted that resistor 23 is sufiiciently small to permitcapacitor 22 to substantially fully discharge to the input of amplifier10 during the interval in which no vehicle is detected by detector D2,regardless of spacing maintained between vehicles in the trafiic stream.

That output voltage from the computer of FIG. 2 represents the ratio ofthe difference between traflic volume sensed by detectors D1 and D2 tothe sum of trafiic volume sensed by detectors D1 and D2 may be shown inthe following manner:

Let

C =capacitance of capacitor 22 Q =charge on capacitor 22 E=negativereference voltage amplitude Hence which can be rewritten as Sincecapacitors 15 and 19 are both charged from output voltage E of amplifiertotal charge applied to the input of amplifier 10 at equilibrium isequal to total charge removed from the amplifier during time T. Hence Bymaking C =C and C =C Equation 10 can be rewritten as Therefore, since CC and E are constants, E is directly proportional to the parameter Itshould be noted that the computer of FIG. 2 provides an output voltagewhich may be either positive or negative, depending upon the relativemagnitudes of trafiic volume sensed by detectors D1 and D2, while outputvoltage produced by the computer of FIG. 1 is always of negativepolarity. As a result, when trafiic volume sensed by detector D1 isequal to trafiiic volume sensed by detector D2, output voltage producedby the computer of FIG. 1 is one-half of its maximum amplitude, whileoutput voltage produced by the computer of FIG. 2 is zero. Hence,relative traflic volume information may be introduced into a singlepolarity or dual polarity circuit, depending upon selection of aparameter computer in accordance with FIGS. 1 or 2.

It should be noted that by opening the series circuit comprisingcapacitor 19, resistor 20 and relay contact 18 in FIG. 2, the parameterV1 is derived. Alternatively, by opening the series circuit comprisingcapacitor 15, resistor 17 and relay contact 18 in FIG. 2, the parameter2 is derived. Moreover, the sign of V in the numerator of Equations 11and 12 may be reversed by coupling front contact 12 to a source ofnegative voltage, while the sign of V in the numerator of Equations 11and 12 may be reversed by coupling front contact .21 to a source ofpositive voltage.

Thus, there has been shown apparatus for computing the ratio of trafficvolume at one or more locations, traffic volume at one or more otherlocations and for computing the ratio of the difference between trafiicvolume sensed at two separate locations to the sum of traflic volumesensed at the tWo locations. The system requires a single operationalamplifier, with passive components supplying the remaining necessarycircuit elements. The system is rugged, stable and requires minimalamounts of power for operation.

Although but several embodiments of the present invention have beendescribed, it is to be specifically understood that these forms areselected to facilitate in disclosure of the invention rather than tolimit the number of forms which it may assume; various modifications andadaptations may be applied to the specific forms shown to meetrequirements of practice, without in any manner departing from thespirit or scope of the invention.

What I claim is:

1. A traffic parameter computer for providing a voltage analog of theratio of traffic volumes at different locations, comprising, detectingmeans situated at each of said locations, an amplifier having an inputand an output, a capacitor shunted between the input and output of saidamplifier, first means responsive to one of said vehicle detector meansfor coupling a pulse of a predetermined amount of said energy to theinput of said amplifier in response to each vehicle detected at a firstof said locations, and second means responsive to the other of saidvehicle detectors for coupling a pulse of energy having a magnitudeproportional to the output of said amplifier from the output of saidamplifier to the input of said amplifier in response to each vehicledetected at another of said locations, whereby the output of saidamplifier is representative of the ratio of the tralfic volumes at saidfirst and second locations.

2. A traffic parameter computer comprising vehicle detector meansmonitoring tratfic at each of at least two locations, an amplifierhaving an input and an output, a capacitor shunted between the input andoutput of said amplifier means responsive to said vehicle detector meansfor one of said locations for coupling a positive pulse of predeterminedenergy content and of predetermined polarity to the input of saidamplifier in response to each detected vehicle monitored at said onelocation, means responsive to said vehicle detector means for the otherof said two locations for coupling a negative pulse having an energycontent proportional to the output of said amplifier and a polarity thesame as that of the output of said amplifier to the input of saidamplifier in response to each detected vehicle at the other monitoringlocation, and means transferring an increment of signal of a magnitudeproportional to the output of said amplifier from the output of theamplifier to the input of the amplifier in response to each vehicledetected.

3. Apparatus for measuring the ratio of trafi'ic volume as a firstlocation to the traffic volume at a second location comprising, firstand second vehicle detectors at said first and second locationsrespectively, signal accumulating means, first means controlled by saidfirst vehicle detector for adding to said signal accumulating means apredetermined uniform increment of signal for each vehicle detected bysaid first vehicle detector, second means controlled by said secondvehicle detector means for subtracting from said signal accumulating.means a decrement of signal representative of the then-existing valueof the signal stored in said signal accumulating means in response toeach vehicle detected by said second vehicle detector, whereby themagnitude of signal stored in said signal accumulating means isrepresentative of the ratio of traffic volumes at said first and secondlocations.

4. The apparatus of claim 3 which further includes third meanscontrolled by said second vehicle detector for subtracting from thesignal in said signal accumulating means the same predetermined uniformdecrement of signal for each vehicle detected by said second vehicledetector as is added by said first means for each vehicle detected bysaid first vehicle detector, whereby the signal stored in saidaccumulating means is representative of the ratio of the difference intraffic volumes at said first and second locations to the sum of thetraflic volumes at said first and second locations.

5. The apparatus of claim 3 in which said signal accumulating meanscomprises an operational amplifier.

6. The apparatus of claim 3 in which said first means comprises, acapacitor, means for charging said capacitor to a predetermined uniformamplitude of voltage, and means controlled by said vehicle detector fortransferring the charge in said capacitor to said signal accumulatingmeans upon each detection of a vehicle by said first vehicle detector.

7. The apparatus of claim 4 in which said signal accumulating meanscomprises an operational amplifier.

8. The apparatus of claim 4 in which each of said first and third meanscomprises, a capacitor, means for charging said capacitor to apredetermined uniform amplitude of voltage which is of opposite polarityfor the respective first and third means, and means controlled by theassociated vehicle detector for transferring the charge in thecorresponding capacitor to said signal accumulating means upon eachdetection of a vehicle by the respective vehicle detector.

References Cited UNITED STATES PATENTS 3,040,983 6/1962 Bigelow 235l96 X3,047,838 7/1962 Hendricks 235l'.24 X 3,048,336 8/1962 Ritzenhaler235183 3,079,086 2/1963 Galli et al 235183 X 3,082,949 3/1963 Barker235150.24

MALCOLM A. MORRISON, Primary Examiner.

I. RUGGIERO, Assistant Examiner.

1. A TRAFFIC PARAMETER COMPUTER FOR PROVIDING A VOLTAGE ANALOG OF THERATIO OF TRAFFIC VOLUMES AT DIFFERENT LOCATIONS, COMPRISING, DETECTINGMEANS SITUATED AT EACH OF SAID LOCATIONS, AN AMPLIFIER HAVING AN INPUTAND AN OUTPUT, A CAPACITOR SHUNTED BETWEEN THE INPUT AND OUTPUT OF SAIDAMPLIFIER, FIRST MEANS RESPONSIVE TO ONE OF SAID VEHICLE DETECTOR MEANSFOR COUPLING A PULSE OF A PREDETERMINED AMOUNT OF SAID ENERGY TO THEINPUT OF SAID AMPLIFIER IN RESPONSE TO EACH VEHICLE DETECTED AT A FIRSTOF SAID LOCATIONS, AND SECOND MEANS RESPONSIVE TO THE OTHER OF SAIDVEHICLE DETECTORS FOR COUPLING A PULSE OF ENERGY HAVING A MAGNITUDEPROPORTIONAL TO THE OUTPUT OF SAID AMPLIFIER FROM THE OUTPUT OF SAIDAMPLIFIER TO THE INPUT OF SAID AMPLIFIER IN RESPONSE TO EACH VEHICLEDETECTED AT ANOTHE OF SAID LOCATIONS, WHEREBY THE OUTPUT OF SAIDAMPLIFIER IS REPRESENTATIVE OF THE RATIO OF THE TRAFFICE VOLUMES AT SAIDFIRST AND SECOND LOCATIONS.